Research on the sensitivity enhanced by optimized multiple slit structure in surface plasmon resonance biosensor for blood glucose detection

Abstract

In today's society, diabetes is emerging as a global issue. Most of the current commercialized blood glucose meter are invasive, and cause pain to the user. Furthermore, a risk of infection exists due to the direct contact of meter parts with skin and blood. In order to overcome these problems, various technologies of non-invasive blood glucose sensor have been investigated. For substitution of blood, non-invasive blood glucose sensors measure the blood glucose from other body fluids, such as interstitial fluid, urine, tears and saliva. Among these fluids, saliva is more advantageous for the measurement as compared to other body fluids. But glucose concentration in saliva is much lower than in blood glucose, thus any measurement equipment needs much higher sensitivity. This thesis involves research on a surface plasmon resonance (SPR) sensor for blood glucose measurement of salivary glucose. A transmission type SPR sensor has the advantage of miniaturization when it is compared to a reflection type SPR sensor. Research on optimization for transmission type SPR sensor components, slit only structure and the single slit structure with grooves have already been conducted by preceding research groups. In this research, a new structure named as multiple slit structure is proposed. The multiple slit structure is optimized by FDTD simulation and fabricated on an Ag surface by focused ion beam (FIB) milling. Performance of the multiple slit structure is evaluated by calculating transmission (T), relative intensity change (RIC), figure of merit (FOM), and it is compared to the single slit structure and preceding research results. The optimized multiple slit structure has five slits and 129% increased transmission and 106% increased $FOM_I$ when compared to the single slit structure. In actual fabricated sensor case, the multiple slit structure has 106% increased transmission and 69% increased $FOM_I$ when compared to the single slit structure. $FOM_I$ increases by 710% when compared to preceding research. In order to increase the sensitivity and selectivity to glucose, dye chemistry that uses glucose oxidase (GOD), horseradish peroxidase (HRP), amplex ultra red (AUR) is applied. In 1mg/dL glucose, RIC is -2.66% without AUR, however, RIC increases to -17.66% with AUR.